Agglomerate including graft copolymers of acylic acid and methyl cellulose and method of making

ABSTRACT

Water-soluble graft copolymers of acrylic acid and methyl cellulose, including water-soluble salts thereof, are useful as binders in the agglomeration of finely divided materials. The graft copolymers are especially useful as binders in the pelletization of minerals and ores, such as taconite.

United States Patent Lang et al. 51 Feb. 22, 1972 [54] AGGLOMERATEINCLUDING GRAFT [56] Relerences Cited COPOLYMERS OF ACYLIC ACID ANDMETHYL CELLULOSE AND METHOD STATES PATENTS ()F MAKING 3,167,525 1/1965Thomas ..260/4l B 3,298,979 1/1967 l-lagemeger et a1. [721 InvemmWilliam Lang 3,370,031 2/1968 Grommets et al Dem", 3,455,853 7/1969Dekking ..260/l7 A x [73] Assignee: International Minerals 8: ChemicalCorporation Pn'mary Examiner-Allen B. Curtis [22] Filed: Sept. 4, 1968Attorney-James E. Wolber and Peter Andress [21] App]. N0.: 757,468 [57]ABSTRACT I Water-soluble graft copolymers of acrylic acid and methylcel- [52] US. Cl. ..75/3, 71/27, 99/2, lulose, including water-solublesalts thereof, are useful as bin- 260/17 A, 0/41 B ders in theagglomeration of finely divided materials. The graft [5 III- CI-copglymers are especially useful as binders in the pelletization [58]Field Of Search ..75/3, 4; 260/17 A, 41 B; of minerals and ores, such astaconite,

21 Claims, No Drawings AGGLOMERATE INCLUDING GRAFT COPOLYMERS OF ACYLICACID AND METHYL CELLULOSE AND METHOD OF MAKING BACKGROUND OF THEINVENTION This invention relates to a process for the agglomeration ofvarious types of finely divided materials. More particularly, thisinvention relates to an improved process for pelletizing metallicminerals and ores resulting in pellets having increased strength andcohesiveness. Still more particularly, this invention relates to the useof water-soluble graft copolymers of acrylic acid and methyl cellulose,including water-soluble salts thereof, as pelletizing binders in such aprocess, which graft copolymers produce pellets of such increasedstrength, cohesiveness and the like that they are attrition resistantand able to withstand mechanical and thermal shock.

The agglomeration of various types of materials is well known. There aremany processes of agglomeration and devices for agglomeration. They allhave in common the physical upgrading in size, density, and uniformityof finely divided materials for better processing, recovery, orhandling, usually by using a suitable binder.

Agglomeration is commercially used in industries where materials areencountered in a form which is too finely divided for efficient andconvenient subsequent processing and/or handling. The material might beencountered in such a finely divided condition because it occursnaturally or is produced in this condition, or because it may have beenreduced to this condition for the purpose of or during prior processing.It may be necessary or desirable to agglomerate the finely dividedparticles into sinters, briquets, o'r pellets for further processing.

The metal-refining industry is an industry where agglomeration isespecially useful. In many metallurgical operations ore is encounteredin a very finely divided condition as a result of being reduced to thiscondition for the purposes of beneficiation. Typical of such an ore istaconite, a very low-grade ironcontaining rock which is reduced to afinely divided condition and then subjected to a beneficiation procedurein order to concentrate the iron and to make available an ore of therequired richness for conventional blast furnace operation. Unless thetaconite which is obtained from the beneficiation process is convertedinto pellets, the finely divided ore presents many dust problems inhandling and may be blown out of the blast furnace by the air andcombustion products sweeping up through the flue of the blast furnace.The same result would occur through the use of flue dust, which, whileit could be collected and reused, nevertheless in subsequent reusewithout being pelletized would again be lost through the flue. In othermetallurgical operations on other ores similar difficulties may bepresent which make it desirable or necessary to have the ore present inthe form of pellets even though it may have been in a very finelydivided form in its preceding processing.

Therefore, while the instant invention is applicable to theagglomeration of a number of different types of finely dividedmaterials, it will be described with reference to taconite pelletizingfor the purpose of illustration. in taconite processing the finelydivided ore is converted into pellets which are almost spherical andhave a diameter varying from about onehalf inch to 1 inch or more. Thesepellets are formed by agglomerating wet taconite in a suitable device,such as by rolling in a balling drum, and the pellets thus formed arethen sintered in a furnace. The pellets become weaker as a result ofbeing dried out during the sintering operation, and as a result may becrushed by the weight of pellets above them when stored in piles. Thesecrushed pellets produce dust which is very undesirable.

A variety of substances have been used or have been suggested for use asbinders in order to give compression or green" strength to the pelletswith concomitant increase in pellet size. Prior art substances such aspickle liquor, lime,

starch and other naturally occurring organic materials have been triedwith little success. These prior art binders either fail to impart the.required green strength to the pellets or commonly fail to increase thepellet size to that sufficient for efficient utilization in thesubsequent blast furnace operation.

Another material which has been commonly used as a binder is bentonite,a naturally occurring clay. The western or natural sodium'bentoniticclays have almost exclusively been used as binders in taconitepelletizing since it has been found that these clays produce pelletswhich are superior to the pellets produced when native or subbentoniticclays are used. The difference in the properties imparted to the pelletsis apparently due to differences in the chemical and mineralogicalcompositions of the clay. Subbentonitic clays are generally calcium ormagnesium varieties of montmorillonite and may contain substantialproportions of nonclay or nonmontmorillonite impurities. The bentoniticclays are natural sodium clays and are sometimes hereinafter referred toas merely bentonitic clays.

The use of clay as a binder for taconite pellets suffers from thedisadvantage of adding silica to the pellets. This silica, the majorchemical component of all bentonites, creates large amounts of unusableand deleterious slag in the blast furnace operation. It,.therefore,becomes necessary to use a calcium carbonate-containing material,preferably limestone, as a flux to remove the silica contained in thebentonite during the blast furnace operation. Another disadvantage inthe use of clay as a binder is tha't'it is generally necessary to use awestern or natural sodium bentonitic clay. This limitation on the typeof useful clay presents a disadvantage in areas where the subbentonitictype of clay is more economically available.

It would, therefore, be an advantage to the art if a binder could beintroduced into the finely divided taconite to be pelletized so as topromote pellet nucleation, allow a rapid pelletization, and impart agreen" or compression strength to the formed pellets to allowconsiderable physical handling without breakdown in pellet size orshape. Another advantage would be realized if this binder could be usedin combination with a western bentonite so as to reduce the quantity ofclay required. Still another advantage would be realized if this bindercould be used in combination with a native or subbentonitic clay inorder to make a clay, which was heretofore unacceptable for use as abinder, a satisfactory binder.

SUMMARY OF THE INVENTION This inventio'n is based on the discovery thatwater-soluble graft copolymers of acrylic acid with methyl cellulose,including water-soluble salts thereof, are eminently useful in theagglomeration of finely divided materials. The graft copolymers of thisinvention may be used either as the sole binder or in combination withbentonite type clays of both the western or bentonitic and native orsubbentonitic types. The graft copolymers and clay combinations areespecially useful as binders in the agglomeration of finely dividedmaterials with which clays have heretofore been used as binders. Whenused in combination with the bentonite-type clays, the graft copolymersare effective to reduce the quantity of clay required and/or to enhancethe effectiveness of the clay as a binder.

Therefore, in one aspect the present invention is directed to a methodof agglomerating finely divided particles using a binder comprising awater-soluble graft copolymer of acrylic acid with methyl cellulose,including water-soluble salts thereof, and the resulting agglomerates.

In another aspect, the present invention is directed to a method ofproducing agglomerates of finely divided particles using a bindingamount of a water-soluble graft copolymer of acrylic acid with methylcellulose, including water-soluble salts thereof, or a combination ofsuch a copolymer and a betonite-type clay, and the resultingagglomerates.

In still another aspect, the present invention is directed to a methodof pelletizing finely divided particles of a mineral or ore such astaconite using a binding amount of a bentonite type of clay and awater-soluble graft copolymer of acrylic acid with methyl cellulose,including water-soluble salts thereof, said graft copolymer beingpresent in an amount sufficient to produce pellets which have a greaterstrength and cohesiveness than if the clay alone were used, and theresulting pellets.

In a further aspect, the present invention is directed to a method ofpelletizing finely divided particles of a mineral or ore such astaconite using a binder consisting essentially of a water-soluble graftcopolymer of acrylic acid with methyl cellulose, including water-solublesalts thereof, and a native or subbentonitic clay, said graft copolymerbeing present in an amount sufficient to enhance the effectiveness ofthe clay as a binder, and the resulting pellets.

in a still further aspect, the present invention is directed to a methodof pelletizing finely divided particles of a mineral or ore such astaconite using a binder consisting essentially of a western bentonite(natural sodium bentonitic clay) and a water-soluble graft copolymer ofacrylic acid with methyl cellulose, including water-soluble saltsthereof, and the resulting pellets.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The graft copolymers of thisinvention are useful as binders, either alone or in combination with abentonite type clay, in processes for the agglomeration of a widevariety of finely divided materials. The material to be pelletized inaccordance with this invention may be almost any type of metallicmineral or ore. For example, the predominant metal constituent may belead, copper, nickel, zinc, uranium, iron, and the like. Mixtures of theabove metals or any other metal occurring in the free or molecularlycombined natural state as a mineral, or any combination of the above, orother metals which are capable of pelletization may be agglomerated inaccordance with this invention. Particularly effective results arerealized in the pelletization of minerals predominantly containing iron.The material to be pelletized may contain iron ore deposits comingdirectly from the mining site, from ore tailings," flue dust, cold andhot fines from a sinter process, or iron ore which is found in a sludgecondition as aqueous iron ore concentrates from natural sources orrecovered from various processes. Any one of these sources of iron orany possible combination thereof may be employed according to theiravailability and particular process setup of the pelletizing unit. ironore or any of a wide variety of the following minerals may form a partof the material to be pelletized: magnetite, hematite, limonite,goethite, siderite, franklinite, ilmenite, chromite, pyrite, and thelike.

Minerals other than metallic minerals which may be agglomerated inaccordance with this invention include phosphate rock, limestone, talc,and dolomite. Still other materials which may be agglomerated inaccordance with this invention are fertilizer materials, such aspotassium sulfate, potassium chloride, and the double sulfate ofpotassium and magnesium; magnesium oxide; animal feeds such as calciumphosphates; carbon black; coal fines; sodium bisulfate; catalystmixtures; refractory gunning mixes; glass batch mixes; tungsten carbide;and antimony.

The material to be agglomerated is desirably about 90 percent -l mesh.Finely divided material having a size of about 90 percent 200 mesh ismost appropriate for the practice of this invention, but material assmall as about 90 percent 325 mesh can be employed.

The graft copolymers which are useful in the method of this inventionare water-soluble graft copolymers prepared by copolymerizing acrylicacid with a minor amount of methyl cellulose, and water-soluble saltsthereof. The amount of the methyl cellulose which is reacted withacrylic acid may vary between about 0.1 and about 10.0 percent,preferably between about 0.25 and about 5.0 percent, based on the totalweight of the acrylic acid used.

The graft copolymerization can be carried out by using wellknownpolymerization techniques. Ultraviolet light or any of the well-knownperoxygen-type initiators, e.g., peroxidefree radical initiators, may beused. The preferred peroxygen-type initiators are hydrogen peroxide andhydroperoxides such as tbutyl hydroperoxide, diisopropylbenzenehydroperoxide, cumene hydroperoxide, l-phenylethyl hydroperoxide, andthe like. Other useful peroxide initiators are diacyl peroxides such asbenzoyl peroxide and acetyl peroxide, and dialkyl peroxides such asdi-t-butyl peroxide and dicumyl peroxide. Still other usefulperoxygen-type initiators include per-salts such as sodium, potassium orammonium persulfate and sodium perborate; the peresters such as t-butylperoxyacetate and t-butyl peroxybenzoate; and the peracids such asperformic acid, peracetic acid, perbenzoic acid, and peroxylactic acid.If desired, Redox-activated systems can be used in accordance with theuseful polymerization practices. Thus, sodium bisulfite-potassiumpersulfate and hydrogen peroxide-ferrous ion systems may be employed.However, the incremental addition of the peroxygen-type initiator ispreferred when a Redox-activated system is utilized.

The quantity of the initiator employed can be varied depending on thereaction temperature and other conditions, but will ordinarily be fromabout 0.0005 to about 0.01 percent, preferably from about 0.002 to about0.004 percent, based on the weight of the acrylic acid.

The temperature of the reaction is not critical and may vary betweenabout 5 C. and about 100 C. The preferred temperature range is betweenabout 40 C. and about C., with a temperature between about 60 C. andabout 70 C. being most preferred. The reaction may be carried out undersuperatmospheric pressure or even under partial vacuum. However, it ispreferred to utilize atmospheric pressure for convenience since thereaction runs very favorably at this pressure.

The graft copolymerization reaction is carried out in an acidic aqueousmedium. The pH of the reaction medium may be any value up to andincluding about 3.5. It is preferred to maintain the pH between about3.0 and about 3.5 for optimum results. In the event the amount ofacrylic acid utilized is not sufficient to lower the pH of the reactionmedium to a value of 3.5 or lower, the desired pH may be obtained by theaddition of a suitable mineral acid such as sulfuric acid, nitric acidor hydrochloric acid.

The reactants and the initiator are combined in the aqueous reactionmedium in any conventional manner. However, the initiator should not beadded to the reaction medium containing only the acylic acid since thiscould cause the polymerization of the acrylic acid in the absence of themethyl cellulose. As illustrative of a suitable manner of combining thereactants, the acrylic acid and methyl cellulose are each dissolved inseparate amounts of water so as to provide homogeneous solutionsthereof. These solutions are mixed and the initiator is then added tothe mixed solution. Alternatively, the methyl cellulose may be dissolvedin water to provide a homogeneous solution to which the acrylic acid andthe initiator are added. Other methods of combining the reactants andinitiator will be obvious to one skilled in the art. Optimum resultswill be obtained if the methyl cellulose is thoroughly dissolved in atleast a part of the aqueous reaction medium before it is combined withthe acrylic acid. Stirring or shaking of the reaction mixture willfacilitate the polymerization and result in more uniform polymers.

The reaction time will vary according to the reaction temperature and/orquantity of the initiator present. in general, the time should besufficient to consume at least percent of the acrylic acid. Toillustrate the variance of the reaction time at different temperatures,polymerization will be evident in about 5 to 7 hours when acrylic acidis reacted at 60 C. with about 1.0 percent by weight of the methylcellulose, based on the weight of the acrylic acid, and 0.002 percent byweight of hydrogen peroxide, based on the weight of acrylic acid, ispresent. On the other hand, polymerization will be complete in about 15to 20 minutes when the reaction is carried out at 100 C. using the samerelative amounts of the reactants and the initiator. Polymerization maybe detected by a change in refractive index, and completion of thereaction may be detected by the absence of the distinctive odor ofacrylic acid.

At the completion of the polymerization reaction, the copolymer thusproduced may be converted to the salt form. This conversion is generallyeffected by neutralization with an appropriate hydroxide. Alkali metalor ammonium salts of the copolymers such as sodium, potassium andlithium salts may be obtained by reacting the copolymers with thecorresponding hydroxide. Where complete neutralization is desired, astoichiometric amount, and preferably a slight excess, of the hydroxideis used. Partial salts may, of course, be produced by using lessthan thequantity of alkali metal or ammonium hydroxide to effect completeconversion of the carboxyl groups.

The copolymers, in either the acid form or the salt form, may beconverted to a dry form if so desired. This may be accomplished byconventional techniques, such as by heating the aqueous solution of thecopolymer in a drum drier at a temperature of about 105 C. to drive offthe water and yield a dry polymer.

The graft copolymers may be used in either the acid or salt form as thesole binder or in combination with a bentonite clay. The combination ofthe graft copolymer and a clay will be especially useful in theagglomeration of materials such as taconite which have heretofore beenagglomerated by the use of clay. Bentonite clays of both the western ornatural sodium bentonitic types and native or subbentonitic types may beused. When a subbentonitic or calcium montmorillonite type of clay isused, the clay is preferably first treated with an alkali metal compoundwhich is water soluble, ionizable, and has an ion capable of reactingwith calcium to form a water-soluble precipitate. Such compoundsinclude, asfor example, alkali metal carbonates, hypophosphates,oxalates, phosphates, silicates, sulfites, and tartrates. Sodiumcarbonate or soda ash is particularly preferred. The amount of thealkali metal compound employed will be somewhat dependent upon theproportion of calcium montmorillonite in the clay. In general, amountsof from about 0.5 to about 6 percent by weight of the clay will be used.The preferred quantities for treatment are from about 2 to about 4percent by weight of the clay.

The amount of the graft copolymer, including salts such as ammonium oralkali metal salts, or combination of clay and graft copolymer added tothe material to be agglomerated will vary according to the particularneeds of the agglomerating operation. In general, satisfactory resultsare obtained when from about 0.002.to about 20 pounds of graft copolymerper .ton of material to be agglomerated and from to about 30 pounds ofbentonite per ton of material to be agglomerated are employed.

When the graft copolymer is to be utilized as a sole binder, i.e., whenno bentonite is employed, the graft copolymer will generally be used inthe amount of from about 0.2 to about 20 pounds per ton of material tobe agglomerated. An amount of from about 0.5 to about 5 pounds of graftcopolymer per ton of material is preferably used in iron orepelletization operations, with an amount in the range of from about 1 toabout 2 pounds per ton being most preferred.

When the graft copolymer is utilized in combination with a bentoniticclay for agglomerating a mineral or ore such as taconite, the amount ofthe clay will be indirectly proportional to the amount of graftcopolymer utilized. A mixture of from about 0.002 to about 0.15 pound ofgraft copolymer and from about 8 to about 30 pounds of bentonitic clayper ton of material to be agglomerated will be typical. When the graftcopolymers are utilized in combination with a subbentonitic clay foragglomerating a mineral or ore such as taconite, the amount of the clayutilized will generally be in the amount of from about l2 to about 30pounds per ton of material to be pelletized. The amount of the polymerused in combination with the subbentonitic clay will be sufficient toenhance the cffectiveness of the clay as a binder, which will generallybe the amount from about 0.004 to about 0.15 pound per ton of materialto be agglomerated.

The only other ingredient required in the process of this invention inaddition to the finely divided material to be agglomerated and the graftcopolymer (possibly in combination with clay) is water. in general,moisture is required to promote compactness and 'adhesiveness of theagglomerates so that they may withstand subsequent handling. The wateroperates in conjunction with the binder to give good binding action. Themixture to be agglomerated will generally contain from about 2 to about20 percent by weight of water, based on the weight of the finely dividedmaterial. A typical moisture content in processes for pelletizingminerals and ores such taconite will be from about 5 to about 12 percentby weight of water, based on the weight of the material to beagglomerated. The water content of a taconite-containing mixture to beagglomerated will preferably be in the range of from about 8.5 to about10.5 percent by weight of water, based on the weight of the taconite.

When the graft copolymer and clay are used in the process of thisinvention for 'the pelletization of iron ore, such as taconite, themixture to be pelletized may also contain a small amount of fluxmaterial chosen from a number of known substances. The presence of thisflux material might be desirable to aid in in the removal of the silicacontent of the clay from the metal meltas slag. A calcium carbonatecontaining substance is generally employed because of availability andlow cost. Among these, limestone or an impure source of limestone suchas calcite is suitable.

in the practice of this invention, the graft copolymer may be added tothe finely divided material to be agglomerated at any time prior to theagglomeration operation. The components of the agglomeration mixture(i.e., finely divided material, water, graft copolymer and clay, if usedin combination with the graft copolymer) may be mixed in anyconventional manner and in any order. However, as hereinbefore pointedout, it is preferred that any alkali metal compound such as soda ash beadded to the clay before the clay is combined with any of the othercomponents of the agglomeration mixture when a subbentonitic clay orcalcium bentonite is used. in addition, when iron ore is pelletized inaccordance with this invention, the graft copolymers arepreferably notcombined with the iron ore until just prior to the agglomerationoperation. The effectiveness of the graft copolymers as a binder mightdeteriorate if the graft copolymers are admixed with the iron ore for asubstantial period of time, e.g., 8 hours, prior to the agglomerationoperation.

Suitable methods for combining the components of the agglomerationmixture will be readily apparent to one skilled in the art. For example,the graft copolymer may be mixed in a dry finely divided form with thefinely divided material to be agglomerated (and 'the clay, if used) toform a composition to which only the correct amount of water need beadded. Inasmuch as the graft copolymers are water soluble in both theacid and salt forms, they may be added in an aqueous solution to the dryfinely divided material to be agglomerated. In still another alternativemethod of combining the components of the agglomeration mixture, theacid or salt form of the graft copolymer may be added in the dry form orin an aqueous solution to clay before the clay is combined with thefinely divided material. When an aqueous solution of the graft copolymeris utilized, the concentration of the solution may be adjusted to yieldan agglomeration mixture of the desired total moisture content.

lnterrnixture of the components of the agglomeration mixture may beperformed by hand, in an internal mixer, in a paddle-type mixer, or in amulling machine. No particular care as to time and temperature of mixingneed be exercised.

No criticality is claimed in the utilization of a particular type ofagglomeratingapparatus, and any of the well-known types of agglomeratingdevices may be used in the process of this invention. For example, theagglomeration may be carried out by a disc or drum pelletizer. Thisdevice, which is especially useful in the pelletization of minerals andores such as taconite, comprises a rotating inclined surface whichagglomerates the mixture into pellets while flowing upon the revolvinginclined surface. Multiple-cone drum pelletizers are particularlydesirable. Other types of agglomerating devices useful in the process ofthis invention are pug mills, compacting and granulating mills,extruders, and the like.

The agglomeration mixture charged to the agglomerating device will thenbe formed into balls or pellets of the desired size. For example, in thepelletization of taconite, the agglomeration mixtUre is charged to adisc or drum pelletizer which is operated to produce balls or pelletshaving a size of about 1 inch diameter. The resulting balls or pelletsare then removed from the pelletizer and fed to a drying oven where theyare dried to a maximum moisture content of about 0.2 percent.

The following nonlimiting examples will serve to further illustrate thisinvention.

EXAMPLE I This experiment was conducted to demonstrate the effectivenessof the graft copolymers of this invention as a sole binder for finelydivided materials. Several quantities of a hematite iron ore concentratehaving a particle size of about 90 percent minus 325 mesh were blendedin a mulling machine and shredder with varying amounts of water and0.075 percent by weight, based on the weight of the ore, of a sodiumsalt of an acrylic acid-methyl cellulose graft copolymer produced asoutlined above.

Pellets were made from each of the mixtures thus prepared by rolling ina 16-inch drum, rotated at 53 rpm. or 225 lineal feet per minute. Ahandful ofa mixture was first rolled until seeds or small pellets wereformed. A small amount of water was added to the pelletizer to aid thegrowth of these seeds. The contents of the pelletizer were then removedand screened to minus 5, plus 4 mesh. The seeds were returned to thedrum and rolled with more of the agglomeration mixture to build theseeds to pellet size. The agglomeration mixture was fed to thepelletizer at a rate to build the seeds to pellet size in about 3minutes. The pellets were removed from the pelletizer and screened tominus 0.525, plus 0.5 inch, and the screened pellets were then tested.

The average moisture content of each quantity of the product pellets wasdetermined by weighing 15 of the pellets, and then drying them at about130 C. for minutes. The dried pellets were rcweighed and the percentmoisture of the pellets was calculated.

The dry compression strength was determined by testing 10 of the drypellets for crushing with a modified Harry W. Dietert Companysand-strength testing machine. The scale was read at the point offracture of each pellet, and the average of the 10 readings wasmultiplied by a correction factorofpi (3.141).

The green compression strength of the pellets was determined by testing10 green pellets taken from the screened product of the pelletizer inthe method outlined above for testing the dry compression strength.

The drop number" of the pellets was determined by dropping 10 greenpellets obtained from the screened product of the pelletizer from aheight of 18 inches upon a hard surface. These pellets were droppeduntil they broke and the average of the number of drops of the pelletswas determined.

The results obtained in this experiment are shown in Table I.

0.075% copolymer 9.1 340 29 24 10.0 3.0 23 31 10.8 3.2 22 60 This dataclearly show that the graft copolymers of this invention are veryeffective binding agents in the agglomeration of finely divided materialover a relatively wide moisture range. The pellets exceeded thespecification minimum commonly used in the taconite industry for pelletproperties using a binder of 12 pounds of sodium bentonite per ton oftaconite, which are as follows:

Green compression strength 2-3 p.s.i. Dry compression strength 8-10p.s.i. Drop number 6-8 EXAMPLE 11 Another series of experiments wasconducted to demonstrate the usefulness of the graft copolymers of thisinvention as binders in combination with clay. The procedure outlined inExample I was followed, except that 0.15 percent by weight, based on theweight of the clay, of the sodium salt of an acrylic acid-methylcellulose graft copolymer was used in combination with a westernbentonite, a well-known commercial binder used in the agglomeration ofiron ore. The bentonite was used in the amounts of 12 pounds per ton ofconcentrate (0.6 percent by weight) which is the amount commonly usedfor bentonite evaluation in the taconite industry, and twothirds thisamount or 8 pounds per ton of taconite (0.4 percent by weight). Inaddition, blanks using the clay without graft copolymers were run atthese clay amounts. The results of this series of experiments are shownin Table 11.

The usefulness of the graft copolymers in this invention in combinationwith. a western bentonite as a binder will be readily apparent from areview of the data of Table 11. For example, it will be noted that thepellets produced using the polymer in combination with 8 pounds of clayper ton of concentrate exceeded the minimum specifications of thetaconite industry for when clays are used in the amount of 12 pounds perton of taconite.

EXAMPLE 111 Another series of experiments was conducted to demonstratethe usefulness of the graft copolymers of this invention for use incombination with a calcium bentonite to produce satisfactory pellets.The procedure of Example 11 was followed except that the clay was acalcium bentonite treated with soda ash. The results of these examplesare shown in Table 111.

In reviewing Table III it will be noted that the pellets produced fromthe graft copolymer-containing polymerization mixture were superior tothe pellets produced when the polymer wasn't present but soda ash wasused in a greater amount.

Although this invention has been described in relation to specificembodiments, it will be apparent that obvious modifications may be madeby one skilled in the art without departing from the intended scope ofthis invention as defined by the appended claims.

What is claimed is:

1. In a method of agglomerating a wetted mass of a finely dividedmaterial, the improvement which comprises the step of adding to saidwetted mass, prior to the agglomeration thereof, at least a bindingamount of a water-soluble graft copolymer or a mixture of said graftcopolymer and a bentonite clay, said graft copolymer being a graftcopolymerization product of acrylic acid and from about 0.1 to aboutpercent by weight, based on the weight of said acrylic acid, of methylcellulose, or a water-soluble salt of said graft copolymerizationproduct.

2. A method in accordance with claim 1 wherein said graftcopolymerization product is an ultraviolet light or peroxygentypecompound induced graft copolymerization product, and from about 0.002 toabout 20 pounds of said graft copolymer per ton of said material andfrom zero to about 30 pounds of a bentonite clay per ton of saidmaterial is added to said wetted mass.

3. A method in accordance with claim 1 wherein said graftcopolymerization product is a peroxide free radical induced graftcopolymerization product, and said wetted mass contains from about 2 toabout 20 percent by weight of water, based on the weight of saidmaterial.

4. A method in accordance with claim 3 wherein from about 0.2 to about20 pounds of said graft copolymer per ton of said material is added tosaid wetted mass.

5. A method in accordance with claim 3 wherein said finely dividedmaterial is a mineral.

6. A method in accordance with claim 5 wherein said bentonite clay is abentonitic clay.

7. A method in accordance with claim 5 wherein said bentonite clay is asubbentonitic clay.

8. A method in accordance with claim 7 wherein said bentonite clay is asoda ash treated subbentonitic clay.

9. A method in accordance with claim 5 wherein from about 0.5 to about 5pounds of said graft copolymer per ton of said material is added to saidwetted mass.

10. A method in accordance with claim 9 wherein said fine- 1y dividedmaterial is an iron ore and said wetted mass contains from about 5 toabout 12 percent by weight of water, based on the weight of saidmaterial.

11. A method in accordance with claim 10 wherein said finey dividedmaterial is taconite.

l A method in accordance wlth claim 10 wherein from about 0.002 to about0.15 pound of said graft copolymer per ton of said material and fromabout 8 to about 30 pounds of a bentonitic clay per ton of said materialis added to said wetted mass.

13. A method in accordance with claim 10 wherein from about 0.004 toabout 0.15 pound of said graft copolymer per ton of said material andfrom about 12 to about 30 pounds of a soda ash-treated subbentoniticclay per ton of said material is added to said wetted mass.

14. A method in accordance with claim 10 wherein said finely dividedmaterial has a size of about percent minus 325 mesh. 90

15. As a composition of matter, an agglomerate of finely dividedmaterial held together by a binder comprising a watersoluble graftcopolymer or said graft copolymer and a bentonite clay, said graftcopolymer being a graft copolymerization product of acrylic acid andfrom about 0.1 to about 10 percent, based on the weight of said acrylicacid, of methyl cellulose, or a watcr-so1uble salt of said graftcopolymerization product.

16. A composition of matter in accordance with claim 15 containing fromabout 0.002 to about 20 pounds of said graft copolymer per ton of saidmaterial and from about zero to about 30 pounds of said bentonite clayper ton of said material and said graft copolymerization product is anultraviolet light or peroxygen-type compound graft copolymerizationproduct.

17. A composition of matter in accordance with claim 16 wherein saidgraft copolymer is a peroxide free radical induced graftcopolymerization product, and water in the amount of from about 5 toabout 12 percent by weight, based on the weight of said material, ispresent.

18. A composition of matter in accordance with claim 17 wherein saidfinely divided material is an iron ore.

'19. A composition of matter in accordance with claim 18 wherein saidagglomerate is held together by from about 0.5 to about 5 pounds of saidgraft copolymer per ton of said material.

20. A composition of matter in accordance with claim 18 wherein saidagglomerate is held together by from about 0.002 to about 0.15 pound ofsaid graft copolymer per ton of said material and from about 8 to about30 pounds of a bentonitic clay per ton of said material.

21. A composition of matter in accordance with claim 18 wherein saidagglomerate is held together by from about 0.004

to about 0.15 pound of said graft copolymer per ton of said material andfrom about 12 to about 30 pounds of a soda ash treated subbentoniticclay per ton of said material.

2. A method in accordance with claim 1 wherein said graftcopolymerization product is an ultraviolet light or peroxygen-typecompound induced graft copolymerization product, and from about 0.002 toabout 20 pounds of said graft copolymer per ton of said material andfrom zero to about 30 pounds of a bentonite clay per ton of saidmaterial is added to said wetted mass.
 3. A method in accordance withclaim 1 wherein said graft copolymerization product is a peroxide freeradical induced graft copolymerization product, and said wetted masscontains from about 2 to about 20 percent by weight of water, based onthe weight of said material.
 4. A method in accordance with claim 3wherein from about 0.2 to about 20 pounds of said graft copolymer perton of said material is added to said wetted mass.
 5. A method inaccordance with claim 3 wherein said finely divided material is amineral.
 6. A method in accordance with claim 5 wherein said bentoniteclay is a bentonitic clay.
 7. A method in accordance with claim 5wherein said bentonite clay is a subbentonitic clay.
 8. A method inaccordance with claim 7 wherein said bentonite clay is a soda ashtreated subbentonitic clay.
 9. A method in accordance with claim 5wherein from about 0.5 to about 5 pounds of said graft copolymer per tonof said material is added to said wetted mass.
 10. A method inaccordance with claim 9 wherein said finely divided material is an ironore and said wetted mass contains from about 5 to about 12 percent byweight of water, based on the weight of said material.
 11. A method inaccordance with claim 10 wherein said finely divided material istaconite.
 12. A method in accordance with claim 10 wherein from about0.002 to about 0.15 pound of said graft copolymer per ton of saidmaterial and from about 8 to about 30 pounds of a bentonitic clay perton of said material is added to said wetted mass.
 13. A method inaccordance with claim 10 wherein from about 0.004 to about 0.15 pound ofsaid graft copolymer per ton of said material and from about 12 to about30 pounds of a soda ash-treated subbentonitic clay per ton of saidmaterial is added to said wetted mass.
 14. A method in accordance withclaim 10 wherein said finely divided material has a size of about 90percent minus 325 mesh. 90
 15. As a composition of matter, anagglomerate of finely divided material held together by a bindercomprising a water-soluble graft copolymer or said graft copolymer and abentonite clay, said graft copolymer being a graft copolymerizationproduct of acrylic acid and from about 0.1 to about 10 percent, based onthe weight of said acrylic acid, of methyl cellulose, or a water-solublesalt of said graft copolymerization product.
 16. A composition of matterin accordance with claim 15 containing from about 0.002 to about 20pounds of said graft copolymer per ton of said material and from aboutzero to about 30 pounds of said bentonite clay per ton of said materialand said graft copolymerization product is an ultraviolet light orperoxygen-type compound graft copolymerization product.
 17. Acomposition of matter in accordance with claim 16 wherein said graftcopolymer is a peroxide free radical induced graft copolymerizationproduct, and water in the amount of from about 5 to about 12 percent byweight, based on the weight of said material, is present.
 18. Acomposition of matter in accordance with claim 17 wherein said finelydivided material is an iron ore.
 19. A composition of matter inaccordance with claim 18 wherein said agglomerate is held together byfrom about 0.5 to about 5 pounds of said graft copolymer per ton of saidmaterial.
 20. A composition of matter in accordance with claim 18wherein said agglomerate is held together by from about 0.002 to about0.15 pound of said graft copolymer per ton of said material and fromabout 8 to about 30 pounds of a bentonitic clay per ton of saidmaterial.
 21. A composition of matter in accordance with claim 18wherein said agglomerate is held together by from about 0.004 to about0.15 pound of said graft copolymer per ton of said material and fromabout 12 to about 30 pounds of a soda ash treated subbentonitic clay perton of said material.